1. Field of the Invention
The present invention relates to a method and an apparatus for manufacturing an electronic device using a roll-to-roll rotary pressing process, which is intended to economically manufacture an electronic circuit device, such as an IC chip, using functional ink and a roll-to-roll rotary pressing process.
2. Description of the Related Art
As well known to those skilled in the art, electronic devices, such as transistors or ICs, form a circuit pattern using a compact crystal structure of an inorganic material, such as metal or silicone. Thus, an important deposition process, such as a sputtering process, is performed under high temperature and vacuum conditions, using expensive precision equipment. Most manufacturing and inspecting operations require a very clean environment. Further, the operations are performed not through a constant continuous production method but through a batch production method having several stages, so that productivity is very low. According to Moore's law regarding technical development speed, which states that the capacity of memory chips to be developed in the future will double every 18 to 24 months, a nano-scale pattern will be developed. In this case, manufacturing costs will further increase. Thereby, the amount to be invested for new installations may reach several trillions of won. Moreover, whenever a pattern forming process using photolithography and an etching process are repeated, many chemical cleaning operations must be carried out, thus incurring a heavy burden for waste-water treatment and pollution prevention.
In spite of high manufacturing costs, silicone semiconductor producing technology must be further developed in order to produce a high density product of a giga or tera grade, because high density products continuously generate good profits. Meanwhile, the production of an IC chip which has a low grade, that is, a kilo-grade, has low economic efficiency. Thus, even if the kilo-grade chip is required, it will not be produced. Even though the silicone semiconductor industry is developing towards nanotechnology, an industry providing cheap middle or low grade microchips must be maintained in order to provide cheap electronic products for general purposes. To this end, an alternative industry is keenly needed.
When new-generation RFID/USN electronic devices, which are most electronic devices for general purposes, are manufactured using current silicone semiconductor technology, manufacturing costs are high. Thus, it is impossible to supply the electronic devices at low cost. Conversely, if an electronic device comprising a printed IC chip is produced at low cost through a printing method, such as commonly used printed material, the electronic device may be supplied at low cost. Current printing technology is highly developed with respect to productivity and quality. Thus, when rotary pressing technology having high productivity is applied to produce a printed IC chip, an RFID tag can be manufactured for one cent or less, so that a price target is easily achieved.
In order to produce an electronic device having micro scale lines through printing, unlike a silicone semiconductor, no matter how simple the function of the printed IC chip is, the material of circuit elements, including a conductor, a semiconductor, and a dielectric, must have properties in order to be sufficiently printable. Since many efforts have been made to develop nano particles of conductive polymers for several decades, various kinds of printing ink (functional ink) have been developed. Hence, recently, there are many attempts to develop a thin film transistor, a solar battery, a light emitting diode, an integrated circuit, etc. through a printing method using the printing ink. However, the production of the IC chip is not easily realized through the printing method using various kinds of functional ink. It is still in an experimental stage, because of complicating factors.
First, the IC chip cannot be produced through printing because of an ink material. Inventive ink material is still in an initial development stage with respect to characteristics, durability, and cost, so that it is unfeasible to use the ink material in practice. That is, the quality of the ink material and production technology therefore are insufficient, so that the ink material cannot be mass-produced. Although the technology for the ink material is advanced and the costs of the material have become low, electronic devices, such as various IC chips, must be produced through a new method using a printing process, and a booming market where products are competitively supplied and demanded must be created so as to rapidly develop the IC chip printing process. Further, if a printer, which is the important element for producing a printed IC chip, is not modified to be suitable for manufacturing IC chips but is a general printer for printing graphics or images, it is impossible to develop or produce a micro printed IC chip as desired.
Among general printers, a representative printer used in the electronic industry is a screen printer. Assuming that an image screen having visual information or the pattern of an electronic circuit have similar resolution of about 200 μm, even a general screen printer may be used as excellent equipment for manufacturing electronic devices. However, if a print having a finer pattern is required, it is impossible to manufacture a desired electronic device using the general screen printer. Thus, recently, the screen printer has been developed into a precision screen printer, thus increasing the resolution and improving a registration function. Thereby, the precision screen printer is useful for forming a pattern having a larger area in a process for manufacturing a PDP or the like. As advanced screen printing technology, another printing method has been proposed, which is called stencil printing. The stencil printing originates from the screen printing method, but uses a thin metal plate in place of a screen plate. The stencil printing method plays an important role as equipment for mounting semiconductor chips. It is a good example of development of the general printer into equipment for producing an electronic device. However, the resolution of the equipment has not reached the resolution required for manufacturing IC chips.
Further, many attempts have been made in a silicone semiconductor industrial field to produce electronic devices using not a stage production process but a roll-to-roll continuous production process. No matter how the precision screen printer or the stencil printer is developed to be generally used for producing electronic devices, it does not overcome the limitation of the stage production process. A roll-to-roll continuous printing process has been already developed. However, unless a new rotary pressing technology and a new ink transfer method for a printed IC chip, which must be fundamentally superior to existing image information printing technology and printers optimized for a person's visual discrimination, are developed, a conventional rotary press cannot be utilized. Thus, like the precision screen printer or the stencil printer, the printing method using the rotary press must be modified so as to be suitable for producing electronic devices.
Recently, an ink jet printing method has been used to provide MEMS characteristics to an electronic device. The ink jet printing method is one kind of direct-imaging printing method, and is carried out in a non-contact manner as follows. That is, ink droplets having a very small size in the pico-liter scale are deposited through a nozzle of an ink jet head on an object to be printed according to a design pattern stored in a computer file at a high discharge speed which discharges several thousands droplets per second. Such a printing method has been rapidly developed for several decades, and is becoming a representative digital printing method which is used in a print field outputting digital file data. In order to perform even a printing test of a conventional printer, a person must master a complicated plate-making operation and a difficult multi-stage control operation for driving the printer. Unlike the conventional printer, a material scientist can easily use the ink jet printer. That is, it is possible to immediately obtain a printed product through the ink jet printing which is automatically driven according to the pattern data stored in a computer, so that such a printing method is the most preferred printing method in the organic semiconductor technology field. However, the ink jet printing method basically uses dot printing technology, unlike other printing methods. Thus, several problems may occur in the application of the ink jet printing method to line pattern printing.
In a detailed description, the ink jet printing method is disadvantageous compared to a typical printing method which is performed in a contact manner using a printing plate, in consideration of a pin hole forming a line using dots, gaps, surface roughness, edge roughness, difficulty in forming lines of various widths, and positional misalignment when repeatedly printing. Further, in the case where mass production is attempted, the movement of many nozzles when a plurality of engine sets comprising a great number of ink jet heads is moved is complicated in comparison with a very simple printing using a printing plate. Hence, it is difficult to obtain uniform print quality, especially when micro printing. As a result, a lot of research has been conducted and a lot of effort has made in order to develop an ink jet printing method that can overcome the above-mentioned problems when printing an organic IC chip.
Recently, as another example, soft lithography, also known as micro contact printing, has been promoted. Soft lithography was invented so as to produce an IC chip circuit having a design rule from 100 to 0.1 μm in an economical manner. The soft lithography is a new printing method which performs line pattern printing using a simple contact-type printing process. However, this method is used as a process replacing only a photolithography process in a silicone semiconductor production process, unlike the original intention. Since the printing method conducts printing using special precision chemical ink which may form a self-assembled monolayer (SAM), the printing of a fine line width at a nano grade as well as a micro grade is possible. A printing plate uses a flexography printing plate manufactured by preparing a concave mold pattern having a fine pattern using a photolithography technique of the existing silicone semiconductor manufacturing process, and pouring silicone rubber into the concave mold pattern. However, the technology making a silicone rubber printing plate having a fine pattern corresponding to a sub micro grade using advanced silicone semiconductor technology, and realizing the pattern of a fine corrosion-preventing film using SAM ink, which is an expensive high-grade material, is used only for producing expensive IC chips. Thereby, this printing method tends to be used for nano-transfer-printing (NTP) technology, unlike its original purpose. This printing method has been developed as technology having higher economical efficiency and productivity in a corrosion-preventing film manufacturing process for a large-sized IC circuit and a nano-grade IC chip, which has not satisfactorily been achieved by current photolithography technology. Therefore, the soft lithography printing method is not printing technology suitable for efficiently producing a printed IC chip that is inexpensive and has a simple function.
Further, a printing method using a precision screen printer provides relatively good results in comparison with the photolithography method, when a plate panel display, such as a PDP or an LCD, which is wide and has a larger area, is manufactured, so that the printing method contributes to this field. The printing method contributing to the field includes a screen printing method, an ink jet printing method, a gravure offset printing method, etc. The gravure offset printing method provides excellent ink transferability when a fragile substrate, such as glass, is printed. Further, since it is possible to use a finely patterned gravure printing plate, the gravure offset printing method is used to manufacture an IC circuit plate having a larger area and serving as an active component for driving the display. Further, the printing method is used to form a color filter element of a display having a large area.
The gravure offset printing method is called a rotary pad printing method. The gravure offset printing method is used in the above-mentioned field, because it is possible to make a fine circuit line pattern having a design rule of several micrometers on a cylindrical printing plate, it is possible to use an elastic blanket made of silicone rubber, which easily transfers ink to a fragile substrate having a large area, like screen printing and ink-jet printing, and 100% ink transferability of the silicone rubber is suitable for electronic pattern printing. However, this is mainly used to overcome an upper area limit in a photoresist patterning process, which is one silicone conductor process. Meanwhile, recently, many attempts have been made to put into practice methods derived from the gravure offset printing method, which is advantageously used to print a fine electrode circuit thanks to the development of conductive polymer ink. However, it may only substitute for photoresist patterning in the silicone semiconductor process, and is only useful as a batch printing method for a substrate having a larger area. Thus, no printing method which supplements the function of the gravure offset printing method has been proposed for making a printing unit, which could thereby economically produce an IC chip in a rotary pressing process, like the present invention.
An advanced printing technology is a newspaper printer. Recently, the rotary offset printing technology for newspaper printing has been developed to the extent that the production speed has reached a current maximum of 25 m/sec (1500 m per minute). To this end, the driving method has recently changed. That is, according to the prior art, a shaft and gears are complicatedly mechanically coupled to one main motor, thus rotating many cylinders of respective units. This has changed to a shaftless system, in which each cylinder is independently rotated by a respective servo motor. A servo driver for the servo motors is controlled via a computer, so that multicolored printing and a post process, such as folding or cutting operation, can be more accurately and consistently achieved at high speed using one printer.
Further, the ink supply amount is automatically controlled by vision control employing a digital camera, and the drive cylinder of each printing unit is delicately controlled with respect to the rotating direction and the axial direction for the purpose of precise registration. As such, mechatronics and automatic control operation have been developed into a system comprising a high technology computer, so that automation having a self-diagnostic function has been achieved. This is the first roll-to-roll production equipment. However, the current rotary press for printing newspaper cannot be used to print an IC chip. The reasons are as follows.
First, the resolution for informational image printing, including newspaper printing, is adapted to a person's visual limits. Thus, it is designed such that the highest resolution is about 100 μm (250 lpi). However, for a transistor, which is an important active component of an IC chip, an organic thin film transistor (OTFT), which may be printed using organic ink, such as conductive polymer or semiconductor polymer, must have a channel length between a source and a drain or a circuit line width of about 10 μm, so as to increase the usability thereof. Thus, the printing resolution realized by the printing technology must be developed to about 10 μm. However, since the current printing technology is set to 100 μm, the technology cannot be applied to print and produce an IC chip requiring a design rule of 10 μm.
Second, regardless of whether the offset printing technology, the gravure printing technology, the type printing technology, or another highly productive printing technology is considered, the image printing technology for visual information has been developed based on dot printing technology. In order to apply the general printing technology to IC chip printing requiring line patterns, many problems of the ink jet printing method must be solved. Thus, new printing technology must be developed to realize line-pattern printing.
Third, general printing, such as color printing, is technology that conducts printing using a distributional arrangement process such that respective dots having different colors printed by one color in different two-dimensional printing units do not overlap each other, if possible. However, in order to produce an IC chip using a contact-type printing process using a printing plate, a technique permitting overlap printing is required in order to realize a three-dimensional MEMS technique. The visible image information printing can utilize a screen distribution technique comprising several dots that use an optical illusion to deceive a person's eyes. Thus, even if the dots are not contiguous, this is allowable to some extent. Further, when one dot overlaps another dot which has been previously printed and is not dry and the resultant color is muddy, this is no problem so long as the muddiness is not detected by a person's eyes. However, the line pattern of the printed IC chip does not tolerate the above-mentioned printing defects, but strictly requires the printing of a pattern and shape having reliable physical parameters. A new print quality standard must be established. That is, printing which produces a line-gain beyond an allowable tolerance, in addition to having the problems of pin holes, discontinuities, roughness, etc., is unacceptable. Further, printing layers printed one by one must be neatly transferred, the physical properties of overlapping printing layers must not be mixed with each other, and insufficient drying, leading to intermixing, is unacceptable.
Fourth, as described above, the print quality of image information is finally determined by a person's eyes, so that it is possible to visually check colors, resolution, or concentration using an optical camera. Since it is possible to measure the colors, resolution, or concentration by sensing light reflected from printed matter, production and real-time inspection may be simultaneously carried out in a printing line merely by mounting a camera on the printer. However, the quality of an electronic device is determined by electronic physical factors, including conductivity, mobility, a dielectric constant, etc., which are measured by direct contact using a probe of an electrode.
When an IC chip is produced through a roll-to-roll rotary pressing process, desired productivity and economical efficiency cannot be achieved unless real-time inspection is conducted through a non-contact type of in-line inspection method, as in general printing. In the present state, the inspection method of the general printing, which measures color, resolution, and concentration, must be indirectly used. The optical parameters of physical factors are appropriately determined according to the ink and print conditions, so that the visual method using a camera is employed.
Fifth, a more precise registration capability is required, in comparison to the conventional rotary pressing technology that prints an object to be printed, which is susceptible to tension, heat, and moisture, like paper and film, using a roll-to-roll process. A precise register control is required to form a fine pattern circuit of the printed IC chip at a predetermined position for respective layers through printing. In other words, a register control which controls an allowable tolerance in a more precise and highly advanced pattern having a resolution of about 10 μm is required.